Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.

Contents

This feature module describes the RADIUS Tunnel Attribute Extensions feature. It includes the following sections:

Information About RADIUS Tunnel Attribute Extensions

RADIUS Tunnel Attribute Extension Benefits

The RADIUS Tunnel Attribute Extensions feature allows you to specify a name (other than the default) of the tunnel initiator and the tunnel terminator. Thus, you can establish a higher level of security when setting up VPN tunneling.

RADIUS Tunnel Attribute Extension Description

Once a NAS has set up communication with a RADIUS server, you can enable a tunneling protocol. Some applications of tunneling protocols are voluntary, but others involve compulsory tunneling; that is, a tunnel is created without any action from the user and without allowing the user any choice in the matter. In those cases, new RADIUS attributes are needed to carry the tunneling information from the NAS to the RADIUS server to establish authentication. These new RADIUS attributes are listed in Table 1.

Note In compulsory tunneling, any security measures in place apply only to traffic between the tunnel endpoints. Encryption or integrity protection of tunneled traffic must not be considered as a replacement for end-to-end security.

Table 1 RADIUS Tunnel Attributes

Number

IETF RADIUS Tunnel Attribute

Equivalent TACACS+ Attribute

Supported Protocols

Description

90

Tunnel-Client-Auth-ID

tunnel-id

Layer 2 Tunneling Protocol (L2TP)

Specifies the name used by the tunnel initiator (also known as the NAS1) when authenticating tunnel setup with the tunnel terminator.

91

Tunnel-Server-Auth-ID

gw-name

Layer 2 Tunneling Protocol (L2TP)

Specifies the name used by the tunnel terminator (also known as the Home Gateway2) when authenticating tunnel setup with the tunnel initiator.

1When L2TP is used, the NAS is referred to as an L2TP access concentrator (LAC).

2When L2TP is used, the Home Gateway is referred to as an L2TP network server (LNS).

RADIUS attribute 90 and RADIUS attribute 91 are included in the following situations:

•If the RADIUS server accepts the request and the desired authentication name is different from the default, they must be included it.

•If an accounting request contains Acct-Status-Type attributes with values of either start or stop and pertains to a tunneled session, they should be included in.

How to Configure RADIUS Tunnel Attribute Extensions

There are no configuration tasks associated with this feature.

Verifying RADIUS Attribute 90 and RADIUS Attribute 91

To verify that RADIUS attribute 90 and RADIUS attribute 91 are being sent in access accepts and accounting requests, use the following command in privileged EXEC mode:

Command

Purpose

Router# debug radius

Displays information associated with RADIUS. The output of this command shows whether attribute 90 and attribute 91 are being sent in access accepts and accounting requests.

RFCs

Technical Assistance

Description

Link

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Feature Information for RADIUS Tunnel Attribute Extensions

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.

Note Table 2 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

Table 2 Feature Information for RADIUS Tunnel Attribute Extensions

Feature Name

Releases

Feature Information

RADIUS Tunnel Attribute Extensions

Cisco IOS XE Release 2.1

The RADIUS Tunnel Attribute Extensions feature introduces RADIUS attribute 90 (Tunnel-Client-Auth-ID) and RADIUS attribute 91 (Tunnel-Server-Auth-ID). Both attributes help support the provision of compulsory tunneling in virtual private networks (VPNs) by allowing the user to specify authentication names for the network access server (NAS) and the RADIUS server.

In Cisco IOS XE Release 2.1, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

Glossary

Layer 2 Tunnel Protocol (L2TP)—A Layer 2 tunneling protocol that enables an ISP or other access service to create a virtual tunnel to link customer remote sites or remote users with corporate home networks. In particular, a network access server (NAS) at the ISP point of presence (POP) exchanges PPP messages with the remote users and communicates by L2F or L2TP requests and responses with the customer tunnel server to set up tunnels.

L2TP access concentrator (LAC)—A network access server (NAS) to which the client directly connects and through which PPP frames are tunneled to the L2TP network server (LNS). The LAC need only implement the media over which L2TP is to operate to pass traffic to one or more LNSs. The LAC may tunnel any protocol carried within PPP. The LAC initiates incoming calls and receives outgoing calls. A LAC is analogous to an L2F network access server.

L2TP network server (LNS)—A termination point for L2TP tunnels, and an access point where PPP frames are processed and passed to higher-layer protocols. An LNS can operate on any platform that terminates PPP. The LNS handles the server side of the L2TP protocol. L2TP relies only on the single medium over which L2TP tunnels arrive. The LNS initiates outgoing calls and receives incoming calls. An LNS is analogous to a home gateway in L2F technology.

network access server (NAS)—A Cisco platform, or collection of platforms, such as an AccessPath system, that interfaces between the packet world (such as the Internet) and the circuit-switched world (such as the PSTN).

virtual private network (VPN)—A system that permits dial-in networks to exist remotely to home networks, while giving the appearance of being directly connected. VPNs use L2TP and L2F to terminate the Layer 2 and higher parts of the network connection at the L2TP network server (LNS) instead of the L2TP access concentrator (LAC).

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